An Exercise
by MrsNoggin
Summary: Sherlock has an experiment in mind and needs a willing participant. Or not so willing. We'll see. Now rated M for John's deplorable vocabulary and maybe a little sexual tension. Nothing toooooo graphic!
1. Explanation

_**A.N.** OK, not really sure where this came from. Just John Watson + treadmill + tension = happiness. It will hopefully end up as four or five short chapters and is just a bit of nonsense. Apologies in advance for any errors in my medical terminology, I'm a bit distracted when it comes to describing John's muscles... _

**_Chapter One - Explanation_**

_DISCLAIMER: None of the characters belong to me, but the treadmill does._

* * *

The flat was quiet. Not silent; John was reading the newspaper and that rustled as he turned pages, and Sherlock was writing long passages on notepad and that made sharp rhythmic scribbling noises. But the sounds were hushed and peaceful, just the way John liked them on a Sunday afternoon. He might even make himself get up in a minute and make some tea. There were some chocolate hobnobs hidden in the back of the cupboard, they might still be there.

"John?"

Oh no. This was going to be bad. He could tell already. Sherlock had that voice on. The one that accompanied slightly widened eyes and the power to persuade and wheedle anything out of anyone.

"No." And that was final. He put the paper down in preparation of leaving the room. Those biscuits were calling.

"Oh."

He sat back again. Was that it? Surely Sherlock wasn't giving up already? No, John knew him better than that. His flatmate may be silent, but he would be planning now, forming some new devious strategy to convince John to perform to his will. Most likely without him even knowing. And so it began.

John stopped wondering what he was going to do and questioned what he was doing right now. It was something scientific, involving calculations and diagrams. He was immediately glad he had refused.

He looked over to the coffee table, curious, but trying not to appear so. Beside the laptop (his) was an open book of anatomical diagrams (also his) and sheets of papers scrawled with drawings and notes (not his) and topped with a photograph of a naked pair of legs (definitely not his!).

Hang on... Yes they were.

Why did Sherlock have a picture of his legs? And how the heck had he snuck that one? He peered around again to try and snatch a glance of the background, but Sherlock snapped the folder shut, giving him a significant look. If he wasn't going to be any part of it then he wouldn't get to see any part of it. The computer was lifted onto Sherlock's lean lap, turned purposefully so John could see nothing of the screen. He felt his eye twitch with the clicks of the keyboard.

A few minutes later, minutes that seemed long to John trying to fight his curiosity, Sherlock spoke again, "Before I agree to this contract at the gym to try and find a willing volunteer, and pay twelve months membership fees upfront as per the sickeningly avaricious terms and conditions, can I just confirm that you are unwilling to assist me in this particular study?"

John sighed, knowing Sherlock's strategy has almost succeeded. Obviously, seeing as he was considering agreeing just to find out what it was all about. "What study?"

Sherlock raised his eyebrows, through presumably not in surprise.

"No, no, no. Don't do that. You have to fill me in on the particulars before I will even agree to consider playing any part in it." He had learned that lesson the hard way.

"If I were to borrow or purchase a treadmill would you run on it for me?"

It was John's eyebrows' turn now. That sounded far too simple. "Elaborate."

"I wish to perform a study in the development of musculature. And I'd much rather do it here than in a gym."

"Method?"

"I would require you to '_run_' twice a day for a minimum of ten days."

"Purpose?"

"To study the movement and growth, mainly of the quadriceps femoris and the gastrocnemius, but the observation will hopefully cover all the major muscles in your legs, and how they change and develop as you become accustomed to the exertion."

"Would you be harassing strangers if I refuse?"

"Undoubtedly."

"What's the catch?" Because there was one. There had to be. There always was. Often more than one. Though it sounded, even to him, as though he were already agreeing to participate. Maybe he was. The idea of being an example of the perfect human form for Sherlock to study hit a chord in him, sending it humming and thrumming. He could do it, sure he could. Unless there was a catch...

"You would be barefoot."

That couldn't be it. That didn't sound too terrible. In fact it made perfect sense; humans were designed to run barefoot. "How much running? How far?"

Ah, judging from the sudden loss of eye contact, _that_ was it. Sherlock shuffled his papers around for a second, "Well, I am, as yet... Uncertain."

John was not fooled. "How far?"

"As far as you can."


	2. Experimentation

_**A.N.** Here it comes - C**hapter 2 - Experimentation**. Poor John. (I think all the chapters might start with 'ex'. Just an extra little challenge.)_

_DISCLAIMER: I still own nobody. Making nothing from writing these stories except the thrill of imagining John on a treadmill._

* * *

Exactly why he had agreed to this, John could not quite recall. He supposed it appealed, in a way, to his doctor's mentality – an opportunity to experiment and examine the properties of the human form. But his own?

He had practised on the new treadmill, done a warm-up before Sherlock appeared, learning the controls and preparing himself. He had taken his own pulse and blood pressure and written it on a post-it for the records. If they were doing this, they were doing it right. But now, with cool grey eyes wandering over his physicality to the minutest detail, any confidence he may have gained had flown out of the door, slamming it behind.

What was he doing? Ten years ago he could have put on a good show. When he was young and fit and in peak condition. Now he was just old and tired, unfit and maybe even a little crippled. As Sherlock knelt in front of him, hooking a silky cool measuring tape around his thigh, he spoke up.

"Maybe I'm not the best candidate for this, Sherlock. What if my dodgy leg screws up the results?"

Sherlock was having none of it, "Nonsense. If anything, variable data will only improve the experiment. I am interested to see if there will be a marked difference between the performance of your weaker leg and its companion. Have you weighed yourself this morning?"

"Yes. Eleven... give or take a couple of ounces."

Sherlock jotted something down and measured the other leg. Three positions on the thigh; the very top where it almost got a bit too... erm... close, the widest part of his rectus femoris, and at the root of the quadriceps tendons. And then around the knee, over the patella. Then three positions over his calf; right under the knee, around the widest section of his gastrocnemius, and midway down the graduation of his soleus. Then around the ankle. Sherlock was nothing if not thorough. John was just staring at the treadmill, wishing he had never agreed to this farce.

"There is an average of almost three quarters of an inch difference over your weaker limb measurements." Sherlock sounded thoughtful. He scribbled down some notes.

"You're working in imperial?"

"Of course not. Far too imprecise."

Oh, John realised, he was converting his findings for him as he went along. John, of course, _could_ work in metric – his job depended on it, but along with the majority of his generation it did not come naturally. It was surprisingly considerate of his friend.

"If we start off at... Then work up to... It would make it..." Sherlock was mumbling to himself. He programmed the machine to the desired incline. "Up you pop then."

"You're staying?" Of course he was; they had discussed it earlier. But, oh God, this was going to be humiliating.

"I need the visual data in my head."

"I know." He did. He was just being silly. For some reason the idea of the slightly younger and much fitter Sherlock watching him thrash himself on a treadmill was humiliating.

But off he went anyway. He started up at a walk, then a gentle jog, slowly ramping it up, jabbing at the speed controls as he stretched out again. He felt his lungs start to contract more forcefully, the slow strain of his legs. His heart rate started to rise. And it felt _good_.

Sherlock's eyes were fixed on John's legs, recording everything precisely for later, his pen scrawling sightlessly over paper, observing and noting everything.

It was a while since John had run like this; aimlessly and without direction. Probably not since those damned physiotherapy sessions, and that had been a trial rather than a pleasure. There had been no steady rhythm like this, no regular beat of footsteps to lose himself in. This was no mad dash through the streets either; he was without desperation or madman to chase.

John had tuned out for a several minutes, slipping into the hypnotic beat of his pulse pounding in his ears, drifting in thoughts. Self-consciousness disappeared and he completely forgot about anyone else being there with him. He visualised country lanes disappearing behind him, the rubber belt of the machine turning into the rough tarmac beneath his feet. The oxygen he sucked in felt fresher, he could almost taste the grass on the air. It was freeing; leaving behind the taint of London, the pressure of the current case (a corrupt police official), the latest rejection of womankind (this one could not be blamed on anyone but him).

He had missed the movement in the room, the slow approach of a thoughtful Sherlock. The curious graze of a cool hand on his burning leg nearly sent him backwards over the belt like a home video comedy clip. Catching himself just in time, he faltered, trying to regain the previous rhythm.

"Sorry, I just needed to..."

"S'fine," John huffed. It was. He was the reason for this whole episode in the first place. If he needed to examine then examine he must. Though John may mourn the loss of his country idyll.

"Don't talk!" Sherlock snapped. "It could affect the data."

John smiled, shaking his head as he pounded on the machine. He was breathing heavily now, panting and aching. He started to consciously use his arms to aid his movements, pumping them forwards and back, feeling an extra twist in his pelvis as he began to force himself onwards. Checking the figures, he realised he had done over two miles. The grin returned. He wasn't in as bad shape as he had feared. He had expected to jog half a mile and collapse in an exhausted walk for the remainder, just to notch it up to one for appearance's sake.

"I'm just going to touch you again, John. But don't speak or slow, just keep going." Sherlock instructed, putting his pad and pen down on the floor and leaning forwards on his knees.

His hand was cold, blessedly so against John's tired leg. He flattened a palm gently over the front of John's thigh, feeling the contraction and release of his muscles. His lips were moving, as he ran over something in his head. He moved his other hand to the back, the biceps femoris and the hamstring tendons. His grip was light, moving with the bunch and spread of flesh, not impeding John's movements in anyway. The back hand slipped upwards, fingers probing in between the lunges of John's leg, finally coming to rest in the dip under the gluteus maximus.

"Sher. Lock." John could hardly breathe now, let alone talk. But this was getting a little too personal for his liking. He would be groping his arse next. Which would result in John landing on it any second.

Sherlock just sent him a warning glare and echoed his examinations on the other leg, "Are you tired?"

John nodded.

"Are you going to fall over or pass out?"

He shook his head. Not quite. Though it might be getting close soon; his legs were starting to shake, almost too heavy to move. He was gasping in air through his mouth, not quite getting enough to fuel his activity.

"Then continue."


	3. Exhaustion

_**A.N - **Chapter 3 - Exhaustion. Even I'm feeling sorry for John now. I can now announce this will end up as five chapters, so we're nearly there! _

_DISCLAIMER: If only they belonged to me, I would run them on treadmills and ogle them every day. Did I say that out loud?! _

* * *

Four miles. He had managed almost five yesterday. Damn.

They were seven days in. Thirteen runs. Several hours of exhausting physical exertion and several more hours of excruciating pain. John lay on the floor, his hands over his face and he gasped in lungfuls of oxygen. The burning in his legs was almost unbearable now, though it had eased during his activity. And his back... God, his back!

Sherlock had his long fingers wrapped around a twitching thigh, measuring and recording the spasms somewhere in his brain. John wondered for a moment if he should point out that Sherlock's planning hadn't taken into consideration the strain his lumbar muscles would be subjected to. Surely he would want to record that too... Then again, there was enough squeezing of personal places going on already, encouraging him any further upwards was not an idea John particularly wanted to entertain.

John had barely managed the cool-down walk necessary to his regime. In fact, he had shaved a whole minute off the end, truly incapable of moving anymore. While his body felt marvellous whilst running, now he could actually cry. He needed a recovery period. He needed some time for his muscles to repair the micro-tears his exercise had caused.

"Sherlock," he panted, wincing at the squeezing ache of his lungs and the dry crackle of his throat, "I need to stop."

"You have stopped," he frowned, pressing his hands in. John jerked at the crushing grip, the burning becoming searing for a second under the contact, and let out a less than manly squeal. He released him in an instant, hands in the air. There was no apology though, just calculation, "Was that painful?"

"Yes," John gritted his teeth. "I mean I need a break. I can't run this evening. I physically can _not_."

Sherlock sat back on his heels, resting one hand back on John's quadriceps, stroking back and forth soothingly. He was thinking. He obviously couldn't bear the thought of jeopardising the experiment, but it seemed he couldn't quite bear the thought of John in this much pain either. John could see the indecision, the almost agony on his face.

"Ok, I'll just rest and see how I feel later," he said softly, reassuringly, knowing exactly how he'd feel later. Exhausted and stiff and nothing like running again.

The rubbing of his leg slowed until only the thumb was moving, sliding up and down the sensitive skin on the inside of his mid-thigh. It was wrong to take any pleasure from the thoughtless contact, but John unconsciously pushed his leg up into the caress, before catching himself and slamming it back down with a painful groan. He knew better than to hope the move had been missed. If he opened his eyes now they would be met with a heavy watching gaze, reading his reaction and working up his reasons. He cracked open an eyelid, despite himself. Yep, there it was.

"John..." It was a quiet whisper and John didn't want to try and understand it. Whether it referred to his physical struggle or his emotional one. The silence grew, longer and more uncomfortable, until Sherlock seemed to shake it off, "No. We'll take a break this evening. I should have seen this coming. Let the muscles repair themselves a little, or you will end up with a serious injury and then the whole thing will be wasted."

John bit back his comment about serious injury, thinking of the twisted ankle from two days ago and the torn muscles of the whole damn experiment, and just thanked the lord that he might get to sit and eat biscuits instead of jogging later. He wasn't sure he would ever recover from this. Sherlock totally owed him one. More than one.

He wondered if he could convince him to run him a bath. And maybe help him into it.

"Make sure you stretch out those thighs." Sherlock patted him, a bit too firmly, and left the room.

* * *

Even in the darkness, John could see the thoughts flickering across the suspect's face. He knew what was coming. And he silently begged him.

_Don't do it. Please don't. Please..._

But he did. John growled in defeat as the man, much younger than him in both years and exhaustion, span on the spot and powered off into the night.

"God fucking damn it!" He hissed and pumped his aching legs into action, chasing the swiftly receding form and the flapping coat tails of his partner. They could not let him get away, he had information and proof that they needed to close the case.

It killed, it actually killed. There was no other way to describe the pain. He could feel the stiff muscles tearing. There was no time for a warm-up, no nice relaxed stretch to convince his body to submit to more exercise. It felt like there was hot blood flowing down his legs, but he knew that was impossible. The adrenaline (if he had any left) had yet to kick in and all he had was the ripping and shredding of flesh and the shaking of his knees. No matter how desperately he tried to force his legs move faster, they refused to listen. It was like a nightmare, coming to life, chasing something just out of reach and being unable to control his body. One of the dreams where you ran and ran as hard as you could and got absolutely nowhere.

He couldn't do it, couldn't do _this_. Sherlock was on his own.

Except he wasn't. He was with John. He had sensed the slowing behind him and turned just in time to watch John stagger sideways and keel over onto the stone steps of the library beside him. Fearing the worst he was alongside him in an instant, running panicked desperate hands over him to find injury. John pushed him off.

"Go, don't lose him!"

"But–" The hands were back, under his jacket and shirt this time, pressing gingerly into his chest, probing fingers feeling blindly for stab wounds or bullet holes or anything out of the ordinary.

"I'm fine." He batted him away, wishing against his will that he didn't have to, "_I'm fine, Sherlock_! Catch the bastard – I'm not doing this all over again."

Sherlock nodded and gave him a last painful pat on the leg before sprinting out of sight.

How _humiliating_. Being left behind. It stung, though not so much as the spasms in his dying muscles.

* * *

At least Sherlock caught the guy in the end. A young man, employed by the corrupt New Scotland Yard official to do some dirty work and drug-running. A satisfactory conclusion to the day, only slightly marred by John's taxi-journey home alone. He was halfway up the dark stairwell, staggering and heaving himself up more by the power of his arms on the balustrade than with his knees, when the door below slammed and a force barrelled into him from behind. If he hadn't been surrounded by the sudden familiar smell of Sherlock, sharp and smothering, with an under-scent of sweat from the chase, he would have pushed back. As it was he did move back, but it was more of a lean. His weight was taken easily and the unseen force behind him propelled him upwards wordlessly.

"Brilliant, John," Sherlock released him at the door, not noticing the small stumble his sudden absence brought about, "He'll talk straight away. We've got him. McAllister has no chance now."

Well good for him, John grumbled inwardly, collapsing sideways onto the sofa, wincing at the creak of his stiff legs. He had five hours until his next run and he full intended to spend them unconscious in the exact position he was in now.

"Are you going to bed?"

"Nope." Simple.

"Because you don't want to?" Sherlock had ducked down beside him and when John opened his eyes he was peering curiously into his face, "Or because you can't get up the stairs?"

"Sod off." He shut his eyes again, afraid Sherlock might offer to help him up there.

"Shall I make you a cup of tea?"

Well, that was a surprise. He frowned suspiciously. "No."

"Why on Earth not?"

"I'm sleeping. And you'll lace it with something anyway, I can tell from your voice."

Sherlock didn't offer hot beverages unless he wanted you to drink them. And he didn't want you to drink them unless there was something in them apart from the usual. It had taken three spiked drinks to learn that – one hallucinogenic that resulted in a petrified sprint around a government laboratory (not that the coffee had actually been to blame, but still...), one experimental laxative that resulted in an embarrassing shift at work (the coffee had _definitely_ been to blame for that one) and one highly illegal stimulant concealed in an innocent mug of tea that had resulted in Sherlock tying up a spectacularly high John in the bathroom until he came down.

He was _not_ drinking anything Sherlock brewed him.

"Sometimes, John, your perceptiveness astounds me," Sherlock stood, giving him a friendly rub on the rump as he passed, "But I was only contemplating sneaking in a couple of anti-inflammatories."

This experiment was really blurring the boundaries of personal space. Since when had it been acceptable to have your hand there? Even in passing...

"I've already exceeded my dosage today, trust me."


	4. Extension

_**A.N. - **Chapter 4 - Extension. Less humour, more tension. I make no apologies..._

_Apart from sorry it took so long. I was distracted by things unconducive to writing. Last chapter will follow VERY swiftly, just to make up for it. _

_Usual disclaimers apply._

* * *

It was raining outside. Nothing so dramatic as a thunderstorm, nor as soothing as light drizzle. Just plain old rain. The front room was dim, but not dark enough to require any source of artificial light. It was drab and dull and perfect.

Sherlock sat in his chair, his chin supported by locked fingers. His eyelids were open but low, flicking slightly as he thought. It was a familiar pose. "I'm not done."

John didn't need to ask him what he meant. He just closed his eyes in defeat. This was torture, and apparently would continue to be so. "How much longer?"

"Two more days should do it."

* * *

The lad had talked, finally. John knew it had been a stressful case for Lestrade, trying to conduct it as quietly as possible, utilising only officers he knew he could trust. It wasn't his division: there was no homicide involved. But he was a trusted detective and his superior had come to him. And he had come to Sherlock. And now it was over and he could relax he had come to John. Nobody helped you relax and feel better about yourself like John did.

"My round," Greg stood up, "Same again?"

"I'd better not." John sighed, "Maybe drop me down to a shandy this time."

"Right. Why?"

"This bloody thing Sherlock's got me doing. Don't ask!" Which of course meant 'ask me immediately so you can reassure me I haven't totally lost my mind'.

"He's interfering with your alcohol consumption now?" Greg laughed, "I know, I know, I'm asking."

"No, he's making me run long distances twice a day and I want to keep my body hydrated and my wits about me." When he said it out loud it sounded silly. Maybe it was silly.

Lestrade patted him sympathetically on the shoulder, "You know you don't have to go along with everything he wants you to do, don't you?"

John huffed out a laugh and shoved him in the direction of the bar. If only he knew.

* * *

Ten days they had done this. To say he had been looking forward to the end would be more than an understatement. And now... There was no end. Not for another two days. He should have finished after the run two hours ago, had his shower and maybe a cold beer and a takeaway to celebrate, but in ten hours he had to get back on that treadmill.

"Do you need another break?" It was an unexpected offer, and very tempting.

"I can't skip another one. It will ruin the whole thing. I'm not wasting all this agony and ruining the results." And secretly he feared a rest might drag it out, require an added day. He may as well get it over with as soon as he could.

John flumped himself down on the sofa beside his flatmate and lifted his legs across him. It was a position they were becoming accustomed to these last few days. Sherlock automatically laid his hands on the skin revealed by John's running shorts, another newly normal arrangement. And John laid his head back as those beautifully skilful long fingers started kneading. Sherlock cupped his hands around the calf, with his palms on the shin and stretched the muscles outwards, plying them firmly with his fingers. Over and over.

Heaven, it was heaven.

And then he repeated his actions on the other leg. It had never been discussed, just happened out of the blue the day before yesterday when John had needed to get his feet up to ease the cramp. Sherlock had been in the way and had ended up with a lapful. And then, of course, had stolen the opportunity for a quick examination, a physical study of the changes in the muscularity using his hands. After noting John's positive reaction to his touch he evolved it into a sports-based massage, working the tightness out of the muscles, killing two birds with one stone. The situation had repeated itself in between every run since. And nobody was complaining.

Although it had never been spoken of, Sherlock had apparently come prepared this time. John laughed at the refreshing silky sensation of warmed body butter on his tight skin. He inhaled and breathed in the scent of cocoa butter on the air. Of course, his friend would not be content with a half-hearted massage for long. If he was going to do it, he was doing it properly. The lotion smoothed the way, and with less skin-on-skin friction it was even better.

When Sherlock reached the prominence of John's Achilles tendon he moved to lay the heel of his hand on the ball of his foot and pushed, teasing and stretching the tight chords. John knew the sound that escaped his larynx was a lot more orgasmic than the situation demanded, but heck, it was damn good. There was a beautiful second where the discomfort hovered on the line of pain before tumbling over into pleasure. Long slender fingers were weaved in between his bare toes for more grip and it took a lot of effort to ignore quite how sexual it felt. Though, if he was honest, the amount of effort it took demanded concentration, and therefore_ ignore_ was perhaps not the right term.

The heavenly hands rubbed their way back up to John's rocklike tensed quads, the pressure increasing. He manipulated the iliotibial tract, stretching and loosening the tendon. He turned his hands at this point, pressing his knuckles into the stiffened flesh, kneading firmly.

"Oh. My. God." John bit out, "If you ever decide to throw in the towel with crime, you could pick up the towel with massage."

"I don't like touching people."

"What's this then?" John chuckled, shifting his prone position to allow easier access to his other leg.

"You're not people," Sherlock wrinkled his nose as if it were perfectly obvious, "You're John."

Right.

* * *

He liked it. It had taken John a long time to admit it, but he felt good. Amidst the pain and complaints, there was pleasure. It was a long time since his body had worked this hard. He had missed it. Every part of him ached, even, oddly enough, his eyelids. But after the initial burning dismount from the treadmill, he could lay on the hard floor and savour the twinge of every muscle. He could fire the directions from his brain to tense each group of muscles, from his feet up through his legs, working over his abdominals and back, down his arms and back up again. A quick flick and then release. Sometimes the rush of blood and spasms of overused nerves that followed would draw a small grunt of something from his throat.

Sherlock watched him go through this every time. He would be perched on the edge of the sofa, recording his latest findings and analysing them as he went. Then John would make a quiet noise as he purposefully pained himself and his eyes would shoot up from the laptop and note which muscle group was causing the sensation. He liked watching. And John liked him watching, even though he himself had his eyes firmly closed. Nothing was ever said. No questions asked. No answers given. A silence only broken by moans of blessed discomfort and the odd shift of skin on the wooden floorboards.

* * *

_I mean it when I say last chapter won't take long. It's all there, just needs a bit of tweaking. As always, reviews fuel the whirring of cogs and tapping of fingers. And if you are following this as a work in progress, THANK YOU! It is that kind of encouragement that keeps it coming. _


	5. Examination

_**A.N. - **Chapter 5 - Examination. Last chapter finally here! The experiment is done, so they can finally stop and return to normal. Brilliant! Or is it? _

_Usual disclaimers apply._

* * *

"You have lost six pounds." Sherlock frowned, curving a line across a graph. "Though more than that if you take into account the muscle gain."

"What about sizes?"

Sherlock just handed over his pad as an answer and let John check out the results graphs. Meanwhile he dropped to the floor and ran his hands over John's legs. It hardly felt odd anymore for this to be an acceptable contact. John supposed it would stop being so soon. Exactly why was he disappointed by that?

"The tone of the muscle is greatly improved."

"Doesn't feel like it to me," John grumbled, turning at the unspoken command of Sherlock's hands on his hips.

"When the stiffness eases it will. Now lift."

John bent his leg at the knee, raising his foot off the floor with one hand on Sherlock's head for balance. He ran his eyes over the charts in front of him. It was an amazingly comprehensive study. Waving the folder in the air one-handed he managed to flip over the top sheet to find scribbled notes detailing his progress. In pencil alongside the professional evaluation were Sherlock's more personal notes. John smiled at those; it was like a teacher annotating a school report. His self-discipline and willpower were noted frequently, alongside his reaction to failing the chase and being left behind.

_J's strength and resolve is admirable. _John grinned at that.

_Prevarication in the form of an extended warm-up implies pain may be more severe that first suspected. J does not hesitate for trivialities. _Well, that was nearly a compliment in Sherlock-world.

_Shows discomfort re: predictable physical reaction to manual muscle manipulation._ What exactly did he mean by that?!

Sherlock twisted the knee in his hands, rotating the joint and checking the movements of John's tendons and ligaments. He put the foot gently on the floor and pushed his fingers upwards.

"Nothing funny," he warned and John knew what was coming. This had become the code for _I'm going somewhere rather private now..._

It was required, he knew, but it didn't make it any easier. John took a second to steel himself and then nodded his assent. He made an effort to read the report, trying to ignore the fingers sliding up his inside thigh. They stroked gently, kneading at the gracilis muscle, feeling the changed chords of flesh, slipping under the edge of his shorts.

And... He failed in to ignore. God, every time. Surely he should be used to this by now; it was an above-board examination. There was no way round it; if Sherlock needed to inspect the physical changes caused by the regime, then this was the only way to do it. But no, John still felt his skin start to tingle, the chemicals releasing, increasing his pleasure receptors. If anything it was occurring faster each time.

"Enough," he mumbled when the movements paused. Sherlock, even crouched behind him and with his mind directed elsewhere, would not fail to notice the reactions happening under his touch. And while he wasn't foolish enough to think Sherlock would care, he was foolish enough to be embarrassed by it.

"Other side?"

"Not right now."

"John," he frowned, "It doesn't bother me."

"Bothers me." Especially after reading the added note about his predictable physical reactions. He changed the subject quickly, putting his foot down literally and figuratively, and quoted "'_Increased stamina in compensation for physical exhaustion is impressive.' _Why, thank you."

Sherlock smiled, but whipped the folder back from John's hands. "I still have to determine whether that is partially deliberate or entirely instinctive."

Most likely both, John thought. A little bit of natural defence, a little bit of vanity. His body needing to seem stronger than it was and John needing to appear... well, who knew what he wanted to appear to Sherlock, and why. It wasn't something he wanted to look into whilst fighting an erection.

"Ready?"

"No." God, the man had no patience. He shifted his weight to the other leg and willed his blood elsewhere.

"Now?"

"Seriously? And don't pout. This is your fault."

"Mine?!" Sherlock didn't pout; he looked affronted instead. "Don't try and place the blame for your–"

"Don't!" John interrupted him, "Don't start putting names to things. It will most definitely not help."

Not even thirty seconds later Sherlock prodded him, "How about now?"

"Oh, for crying out loud! Fine! Just stay below the shorts..."

* * *

Sherlock knew that John hated the treadmill. He could almost understand it, were it not an inanimate object, used only as a tool and therefore incapable of earning said sentiment. John spent all his time in the living room resolutely _not_ going near it, or touching it, or even looking at it.

He was done, he had said. Finished. He had completed his trials for Sherlock's experiment. Read the typed up report. And he refused to go near the damn thing ever again. He might even put it on eBay right now, just to cement the matter. Or that was what he said.

Which was why, as he climbed the stairs to the flat in his usual stealthy manner, Sherlock was surprised to hear an unmistakeable sound. The continuous skimming of a wide rubber belt circulating, punctuated by the rhythmic pounding of feet and the puffing of air being inhaled and exhaled through an open mouth.

John was running.

And he was glorious, Sherlock thought as he breached the doorway and took in the view. He had never been so glad of John's agreement to anything before. Watching him working his body on that machine had been the most enjoyable of any of Sherlock's experiments. Ever.

He had designed the study with simple knowledge as the aim. He wanted to _know_, that was all. Wanted to learn how long it would take muscles to significantly develop in a regular exercise routine without any specific intention for them to do so. Legs were evolved to run, so how would they react to actually doing it? Then John's insecurities had surfaced, and they had to be dealt with. And then he realised he was enjoying it, watching and learning his friend, and so more detailed examinations were required. Then he realised John was enjoying it too, no matter what he said, hence the extension. In the end neither of them had actually wanted to stop, despite John's protests to the contrary.

The shock on John's face was almost comical as he noticed his flatmate in the doorway. He jabbed at the pause button and slowed to a walk before stopping completely.

"I thought you were out for the morning?"

"Yes."

John gave a guilty smile and stepped off the treadmill, watching curious eyes as they skated his legs, absorbing the tensing and flicking of muscle. Sherlock wanted to feel that, he wanted to place his palm over that twitching flesh and feel it against his skin. It had been three days since his last examination of John. Three very long evenings of awkwardness, where Sherlock's hands had found themselves wandering to rest on legs that did not belong to them and where John found himself not kicking them off. He had never found anything about legs remotely attractive before two weeks ago. But now...

"I was up to three miles." John stated, breaking the silence, "I'll get in another mile and then I need to do a cool down."

"Yes." If only Sherlock had an excuse to observe. Could he find one? Or position himself at the kitchen table so he could see. There must be a way. There was always a way.

"Will you watch?" The intonation of John's voice was clear. It was not a question of Sherlock's intentions. It was a request.

"God, yes!"

* * *

_Well I had a** great** time writing it, hope you've enjoyed reading it. If you have, drop me a review and let me know! Cheers me dears x_


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